The monitoring of the level of glucose or other biochemicals, such as lactate, in individuals is often important. High or low levels of glucose or other biochemicals may be detrimental to an individual's health. The monitoring of glucose is particularly important to individuals with diabetes as they must determine when insulin is needed to reduce glucose levels in their bloodstream or when additional glucose is needed to raise the level of glucose in the bloodstream.
Conventional techniques for monitoring blood glucose levels currently include the periodic drawing of blood, the application of that blood to a test strip, and the determination of the blood glucose concentration using electrochemical, calorimetric, or photometric methods. This technique does not allow for continuous monitoring of blood glucose levels, but must be performed on a periodic basis.
A variety of other devices have also been developed for continuous monitoring of analytes in the blood stream or subcutaneous tissue. Many of these devices use electrochemical sensors which are directly implanted in a blood vessel or in the subcutaneous tissue of a user. However, these devices are often large, bulky, and/or inflexible and many can not be used effectively outside of a controlled medical facility, such as a hospital or a doctor's office, unless the user is restricted in his activities.
The user's comfort and the range of activities that can be performed while the sensor is implanted are important considerations in designing extended-use sensors for continuous in vivo monitoring of the level of an analyte, such as glucose. There is a need for a small, comfortable device which can continuously monitor the level of an analyte, such as glucose, while still permitting the user to engage in normal activities outside the boundaries of a controlled medical facility. There is also a need for methods that allow such small, comfortable devices to be relatively inexpensively, efficiently, reproducibly and precisely manufactured.
A significant problem in the manufacture of in vitro electrochemical sensors has been the inability to manufacture small electrodes with reproducible surfaces. Present techniques for printing or silk screening carbon electrodes onto substrates yield electrodes with poorly defined or irreproducible surface areas and conductivities, particularly at trace widths below 250 .mu.m (10 mils).
Small sized non-electrochemical sensors including, for example, temperature probes, would also be useful if they could be reliably and reproducibly manufactured. A process for the manufacture of small sensors with reproducible surfaces is needed.